1. Field of the Invention
The present invention relates to a control system for controlling engagement of an automotive clutch which is disposed in a power transmitting path from an engine to driven road wheels for controlling transmission of engine power through the power transmitting path.
2. Description of the Prior Art
Automotive clutches are usually disposed between the output shaft of an engine and the input shaft of a transmission for controlling transmission of power from the engine through the transmission to driven road wheels. Such an automotive clutch has heretofore been used as a clutch associated with a manual transmission, and engaged and disengaged in response to operation by the driver of the clutch pedal when the automobile is to be started or stopped or a shift is to be made by the transmission.
Automatic transmissions are generally combined with a torque converter coupled to the output shaft of an engine. However, some recent automatic transmissions are combined with automotive clutches. There have been proposed various control systems and methods for automatically smoothly and quickly engaging and disengaging automotive clutches that are associated with automatic transmissions.
For example, Japanese patent publication No. 62-47742 discloses a clutch control apparatus having an actuator which operates in a direction to engage a clutch. When a negative rate of change of the rotational speed of the engine is detected, the operation of the actuator in the direction to the clutch is stopped and the actuator is held in the stopped condition. When a positive rate of change of the rotational speed of the engine is detected, the actuator is activated in the direction to engage the clutch.
When the rate of change of the engine rotational speed becomes negative, i.e., when the engine rotational speed changes so as to be lower, the operation of the clutch to engage itself is interrupted to prevent the engine rotational speed from being decreasing excessively. Therefore, insofar as the rate of change of the engine rotational speed is positive, i.e., the engine rotational speed monotonously increases, the clutch is controlled to engage itself based on the characteristics of the actuator. In the event that the output power of the engine varies, however, it is difficult to control the clutch for smooth engagement because the engine rotational speed tends to fluctuate.
Japanese utility model publication No. 84-21025 discloses an apparatus for controlling engagement of a clutch of an automobile. When the clutch is connected by an actuator to start the automobile, the apparatus compares a predetermined target rate of change for the engine rotational speed with the actual rate of change of the engine rotational speed, and corrects the amount of operation of the clutch based on the result of comparison to cause the actual rate of change of the engine rotational speed to approach the predetermined target rate of change for the engine rotational speed.
The target rate of change for the engine rotational speed is a function of time. Since the torque that is transmitted through the engaged clutch varies with time, the transmission tends to be subject to shocks while gear shifts are being made and when gear shifts are completed.